Move remaining app_api imports out of inference_api to complete service decoupling

[colinmxs]

Summary

The Inference API (inference_api) still has direct Python imports from app_api modules. This was originally a much larger problem (7+ modules), and most have been migrated to apis.shared. Three imports remain and should be moved to complete the separation.

Remaining Imports

In backend/src/apis/inference_api/chat/converse_routes.py:

from apis.app_api.costs.calculator import CostCalculator
from apis.app_api.costs.pricing_config import create_pricing_snapshot

# Lazy import inside _validate_api_key()
from apis.app_api.auth.api_keys.service import get_api_key_service

Impact

• Inference API Docker image must include app_api code
• App API log namespaces (apis.app_api.*) appear in AgentCore Runtime CloudWatch logs
• Changes to app_api cost or auth modules can break inference_api
• Cannot test inference_api in true isolation

Proposed Fix

Move the remaining modules to apis.shared:

1. apis.app_api.costs.calculator → apis.shared.costs.calculator
2. apis.app_api.costs.pricing_config → apis.shared.costs.pricing_config
3. apis.app_api.auth.api_keys.service → apis.shared.auth.api_keys (or have inference_api validate API keys via an HTTP call to app_api)

Update imports in both app_api and inference_api to use the shared location.

Context

This is the last piece of a long-running effort to decouple the two services. The original issue (identified Jan 2025) had 7+ cross-service imports. Most were resolved by creating apis.shared.sessions, apis.shared.files, apis.shared.rbac, etc. These three are the stragglers.

Acceptance Criteria

• No from apis.app_api imports exist anywhere in backend/src/apis/inference_api/
• Cost calculator and pricing config live in apis.shared
• API key validation either lives in apis.shared or uses an HTTP call
• Existing tests pass
• Inference API Docker image can be built without app_api source (stretch goal)